Impact of submerged macrophytes on fish-zooplankton-phytoplankton interactions : large-scale enclosure experiments in a shallow eutrophic lake

摘要: SUMMARY 1. The impact of changes in submerged macrophyte abundance on fish-zooplankton-phytoplankton interactions was studied eighteen large-scale (100 m2) enclosures a shallow eutrophic take. macrophytes comprised Potamategon pectinatus L., P. pusillus L. and Callitriche hermaphroditica while the fish fry stock three-spined sticklebacks, Gasterosteus acuteatus roach, Rutilus rutilus L. 2. In absence zooplankton biomass low dominated by cyclopoid copepods regardless density, phytoplankton biovolume high (up to 38 mm31) small pennate diatoms chlorococcales. When lake volume infested (PVI) exceeded 15–20% density below catch per unit effort (CPUE) 10 (approx. 2 m−2), planktonic cladoceran relatively large-sized specimens, fast-growing flagellates. At higher densities, average cladocerans decreased shift cyclopoids occurred, increased markedly became cyanophytes dinoflagellates. 3. Stepwise multiple linear regressions log-transformed data revealed that Daphnia, Bosmina, Ceriodaphmia Chydorus were all significantly positively related PVI negatively or x fish. individual fish, but unrelated PVI. Calculated grazing pressure Accordingly biomass. Cyanophytes chryptophytes (% biomass) Chlorococcales PVI, contrast cryptophytes zooplankton. 4. results suggest predation has less community more structured environment beds, particularly when exceeds 15–20%. They further refuge capacity decreases with increasing (in our study above approximately CPUE). Provided planktivorous is not high, even improvements may have substantial positive zooplankton, leading lower water transparency. However, at densities effect seems no major mediated effects enhanced growth are be expected.